Nonlinear time reversal signal processing techniques applied to acousto-mechanical imaging of complex materials

Abstract

Recent ten years have seen considerable development of experimental techniques for improving nonlinear NDT methods and harmonic imaging derived from Nonlinear Elastic Wave Spectroscopy (NEWS). Diagnostic ultrasonic imaging based on higher harmonics yields, among others, a better resolution in view of the decreased wavelength in comparison with the fundamental. Furthermore, using symmetry invariance, nonlinear Time Reversal (TR) and reciprocity properties, the classical NEWS methods are supplemented and improved by new excitations having the intrinsic property of enlarging frequency analysis bandwidth and time domain scales. The purpose of this paper is to present the extension of TR-NEWS for skin aging characterization using the Nonlinear Time Reversal signal processing tool known to localize, in a complex medium, sources of nonlinearity potentially responsible of complex material aging. Linear and nonlinear behavior of skin elasticity is measured locally thanks to an acousto-mechanical loading of the skin conducted with INSTRON loading machines specifically optimized for biomaterials. Hysteresis behavior coming from the complex loading of the skin has been identified with PM-space statistical approach, usually associated to aging process in NDT. Phenomenological hysteretic parameters extracted will be presented and associated to standard parameters used for skin characterization.